The seismic swarm continues with the first occurrence of a widely felt magnitude 4 quake last night at 9:56 pm local time, the strongest so-far in the current swarm. The quake was about 10 times larger than the previous largest-so-far quake, a magnitude 3.3 event at 6.41 pm on 19 March.
While the numbers of quakes has been lower in the past few days, it should be taken into account that last night’s quake accounts for approximately the same seismic energy as all quakes during the past 7 days combined. This is because magnitude is a logarithmic scale: one magnitude 4 earthquake is approx. equivalent to 30 quakes of magnitude 3, or 1,000 magnitude 2 events.
Whether this marks a shift in the underlying processes, and whether it is tectonic in origin or caused by magmatic processes or a combination of both, remains unclear.
There were no damages reported by the magnitude 4 earthquake, but authorities and local population remain alarmed because the potential of stronger quakes and/or a volcanic eruption in the near future remains real.
